3. Later I prepared skirt (it was hardest part of work).

In object selection mode select belt and ruffles and in select menu choose "hide selected"

3.1 Using edge select mode I selcted only one horizontal edge few lines under top of skirt. Then press "l" ("L" without "shift") and you should have vertical loop under belt. Then  press "shift" + "L" what change edges selection to polygon selection (see pict). If wings choose polygons under loop do not worry press invert (ctrl shift "I").

Now you can make selected polygons "hole" (RMB in polygon mode)